1. Field of the Invention
The present invention relates to an energy storage device, and more particularly to an energy storage device that maximizes the utilization of the inside of a housing by the improvement of an inner structure thereof and also ensures the reliability by keeping an inner pressure below a certain level.
2. Description of the Related Art
Generally, representative examples of a device storing an electric energy are batteries and capacitors. Among them, a capacitor is an energy storage device, which is called a ultra capacitor or a super capacitor and has features in between an electrolytic condenser and a secondary battery.
Such an energy storage device makes side reactions at an interface between an electrolyte and an electrode when being misused with an overvoltage or the like or used for a long time at high temperature, and gas is generated as a byproduct accordingly.
Considering the generation of gas, a conventional energy storage device is designed to have some space between an electrode unit and an inner side of the housing of the energy storage device.
However, in a case where the energy storage device is used for a transportation means such as a vehicle, the electrode unit in the housing may be shaken right and left due to an external force such as vibration, and accordingly the electrode unit or a lead wire connected thereto may be broken, which results in the deterioration of life or reliability of the energy storage device.
In addition, in a case where the inner pressure of the housing keeps increasing due to the generation of gas, the housing may swell out, or gas may be leaked at a weak region of the housing, which may cause explosion.
In order to prevent such explosion caused by the generation of gas, a notch structure is formed in a partial region of the housing of the conventional energy storage device, so that the notch is fractured at a pressure over a certain level to allow the relief of pressure.
However, in this case, the housing is kept in an opened state after the notch of the housing is fractured, which may seriously deteriorate the performance of the energy storage device due to the leakage of electrolyte or the introduction of impurities.